1. Field of the Invention
The present invention relates to infinitely variable transmissions (IVT""s) and relates particularly, but not exclusively, to the supply of hydraulic actuation and cooling fluids to the roller actuation pistons and rollers provided therein.
2. Discussion of Prior Art
Presently known IVT""s, such as that disclosed in GB-A- 2260583 comprise a pair of input disks and a pair of output disks mounted on a common axis X in order to define a pair of toroidal cavities in which are situated a plurality of variable position rollers employed to transmit motion between the input and the output disks. The rollers are hydraulically controlled by means of double acting hydraulic control pistons which employ the higher and the lower pressures within an associated hydraulic circuit to control the position of the rollers within the variator. In some arrangements, one roller within each toroidal cavity set forms the master roller and the remaining rollers are similarly provided with hydraulic fluid and form slave rollers, the orientation of which follows that of the master roller. In other arrangements two rollers within each cavity are employed as the master rollers. The master and slave rollers in each cavity are equi-spaced around an outer diameter in a manner well known in the art and shown in FIG. 2 of the present invention.
The supply of hydraulic fluid to the master and slave rollers presently requires the outer casing of the IVT to be provided with the various passages which must be precision cast, drilled, cross-drilled or otherwise machined. Alternatively, expensive and vulnerable external piping may be required.
In some applications it may be difficult to provide the complex network of hydraulic passages whilst meeting the desired cost, accuracy and performance requirements. Additionally, the friction losses within individual passages often varies depending on the length, surface finish and straightness of each passage. In some cases this could result in different pressure drops along the said passages and in different pressures being supplied to each roller control piston, thereby compromising the precision of the roller control system.
It is an object of the present invention to provide an IVT assembly which reduces and possibly eliminates the problems associated with the above-mentioned arrangement.
Accordingly, the present invention provides an IVT assembly comprising an outer casing and a plurality of hydraulically operated roller control pistons supplied with hydraulic fluid from a source thereof, via an hydraulic supply manifold, characterized in that said outer casing comprises a split casing and in which the supply manifold comprises a channel within a surface of the casing formed by said split.
Advantageously, the supply manifold comprises two channels, for carrying fluid at pressure, both of said channels being operably connected to one or more of said pistons for the supply of fluid thereto.
Preferably, the first, and the second pressure channels are radially displaced relative to each other.
Advantageously, the supply manifold further includes a lubrication channel, for supplying lubrication within the IVT.
Advantageously, the lubrication channel is radially outward of said first, and second channels.
In a preferred arrangement the IVT comprises two pairs of input and output disks. each pair having sandwiched therebetween a plurality of rollers operably connected to said hydraulically operated roller control pistons, in which the pistons of each input/output disk pair are paired for the purpose of hydraulic fluid supply with a corresponding piston for the other input/output disk pair.
In the particularly advantageous arrangements the pistons of one or more paired pistons are on opposite sides of said split line.
Advantageously the pistons of one or more paired pistons are equi-spaced from the split line, thereby to facilitate maintenance of substantially the same pressure drop within the manifold
In one arrangement the manifold comprises channels formed in one or both of the faces formed by said split in the casing.
In an alternative arrangement the manifold comprises channels formed in just one of the faces formed by said split in the casing.
In certain arrangements, it might be desirable to include a sealing member, such as a gasket, between the faces of the casing.
Conveniently, one or more of the channels includes an extension portion extending into said casing and away from an associated surface thereof, thereby to connect said channel with an appropriate portion of the hydraulic control piston.
Conveniently, the longitudinal axes L of the pistons are angled at an angle xcex8 relative to the plane P of the split in the casing.